Small PS2 2.4 volt batteries

There isn't any.  The battery discharges at a somewhat constant voltage so it's meaningful to measure it's capacity as how much current it delivers for how long.   OTOH the voltage on a capacitor discharges with a relatively steep downward sloping voltage.  For it to work in the PS2-3V system, that's why it needs to charge up to about 5V.  If it only charged up to 2.4V, the voltage would drop out too soon upon discharge unless you had a ginormous amount of Farads.

Due to the way the PS2-3V power supply takes power from the battery or capacitor during shutdown (a so-called switching stepup regulator), it is practical to compare the usable energy stored in the two methods.  So if you measure the energy delivered by the capacitor as it decays from 5V to, say, 2V...and compare that to the energy of the 700mAHr 2.4V battery, I calculate the 1.5F capacitor has an equivalent rating of "only" 2 mAHr!  Given a shutdown time of, say, 10 sec, this means the capacitor can deliver just under 1 Amp for that interval which actually sound about right if I recall the data from the previous threads.

Which is why I have been using the 2.5F capacitors lately.  They can maintain the voltage above the threshold where audio amp output is reduced.  They just seem to take a few seconds more to clear the threshold on start up.  I probably should collect some empirical data.  G

Stan, do you think that the shutdown process and accompanying sounds draw that much---1 amp?

I would also be surprised if the charge circuit in the PS2-3v system gets up to 5 volts, unless there's a lot of IR drop when a battery is connected.

GGG: If, as GRJohn indicates, a 1.5F can keep the sounds alive, then a 2.5F should do the job with some time to spare.  MTH tells me the test is whether the battery or capacitor can "keep the board alive long enough to play the full shut down sounds."

When one powers up a unit with a 2.5F capacitor, there is essentially a dead short for a few milliseconds.  Can this harm the charging circuit?

Let's say the audio output is 2 Watts which is a number people seem to use.  If you only have 2.4V to start with, you need 1 Amp of current considering power conversion losses when trying to double the voltage to the 5V or so that the audio system needs.  Then you add the processor power requirements and it's not hard to imagine such currents.

Pretty much all charging circuits are configured as current sources so even a dead short does not damage the circuit.  As with any charging circuit, the design surely accounts for user error such as a short or plugging the battery in backwards.  Again a current source design handles this situation.

The 5V "open-circuit" (unloaded) voltage of the PS2-3V charging circuit has been discussed before.  Take a voltmeter and hook it up to the battery terminals with nothing connected and if you find otherwise you have a busted charger.  Or have GGG or GRJ measure what the voltage charges up to on their 1.5F or 2.5F capacitors..

RJR,  I have posted this information before.  Stan is correct.  If you measure the voltage at the charge port without a battery you will read 5V, if you plug in the battery it stabilizes around 2.7V (battery plus some).  An uncharged capacitor and it will go to zero and you can watch it charge all the way to 5V.  The source of charging is the 5V power supply that powers the circuit board.

I believe the logic handles the charge current to cover the temporary short at the beginning of the cycle.  That FET can be damaged though, so an extended short or a problem with the inductor boost/buck can cause a failure if the condition is allowed to exist for an extended time.  I have a bench power supply used to test processors that has had charging/battery backup components changed at least 3 times.  G

What's an " inductor boost/buck"?

There is an inductor coil that is shorted to ground to generate about 2.5V charge on the inductor.  When the AC is cut off the stored energy of that inductor is combined with the 2.4V battery to produce the 5VDC for the 7-10seconds of shutdown sounds and memory transfer.  G

http://en.wikipedia.org/wiki/B...80%93boost_converter

GGG, thanks for the description and the link.

There's always something new to learn on the forum.

Thanks for the tips.   I've ordered the parts and will soon build about 20 BCR's.   Tired of dead batteries!

If all goes well I'll buy another batch to replace all the batteries in everything I own.

If anyone is looking for a collection of different size 2.4 NiMHs, here's a link I cam across this morning.  They have as small as 1/3 AAA, 160 mAh.

www.onlybatterypacks.com

{Edited to correct typo noted by GRJ in next post}

A good link would help.

http://www.onlybatterypacks.com/

That site also has another name & link. 

http://www.maxxpacks.com/produ...amp;products_id=1234

If you go to that site, in the middle of the page there is a table, with photos, listing all the types of connectors one can order on the batteries.  I don't recognize any as being what MTH uses, but maybe someone in forumland recognizes it. ???????

Looks like they were close with one of the Molex plugs, but they have the wrong gender.

I thought it was interesting that MTH uses male plugs on its 3-volt batteries leads.  I though the standard was to use female sockets to lessen the chance of shorts.  This does men I can use the plugs on bulbs on battery leads.

I think the MTH situation is a unique case as the board supplies power as well.  I suspect they decided to protect the expensive circuitry and not the cheap battery with the female connection.

FWIW, they also have bulbs and smoke units with with the female plug as the standard, the male pins are coming from the board with the light and smoke power.